Various types of apparatus have been proposed to test breathing response of patients. One such apparatus is known under the name "Astograph". The patent literature also describes apparatus of this type, see, for example, German Utility Model DE-GM No. 79 14 971 U1.
Patients who have asthma have intervals free from attacks; even in those intervals, however, the bronchial system is excessively sensitive to external irritants, for example various types of aerosols. It is possible to trigger a bronchial spasm in such patients by controlled inhalation of substances to which the patients are allergic, or to other particularly active substances. Such spasms can be determined by sensing an increase in resistance in the airways of the patient. This resistance increase is reversible. It is desirable to be able to determine particular substances which cause excessive irritation, so that treatment can be devised for healing or at least reducing the debilitating effects of such irritants. It is thus necessary to be able to determine to which substances the patient is allergic, that is, which substances trigger asthmatic attacks. This has been done, usually, by means of an asthma-provocation test, in which the patient is asked to breath an aerosol which contains a substance to which he may be allergic in atomized form, for example as prepared or provided by a small fog generator.
The usual method of testing the patient was this: During a predetermined period of time, which covered a substantial number of breathing cycles, that is, inhaling and exhaling cycles, an allergen-aerosol was also permitted to be inhaled. Thereafter, the air flow resistance was measured. If the patient did not have an adverse reaction, the concentration of the allergen was increased, and the test repeated, until a certain air flow resistance was exceeded. The referenced German Utility Patent DE-GM No. 79 14 971 U1 describes an apparatus in which the flow resistance of the airways of the patient can be measured almost continuously during the inhalation phase of the breathing cycle. A valve was placed between the atomizing substance and a mouthpiece which the patient used, and which opened upon breathing-in or inhalation by the patient; a branch line was taken off between the valve and the mouthpiece which was connected to a measuring device to measure the flow resistance of the airway or air path upon exhalation. Such a device is capable of rapidly determining even a tendency to obstruction of the airway or pulmonary path of the patient, that is, an initial obstruction or beginning of obstruction condition, so that, by quick application of a counter-acting medication, formation of a severe obstruction could be promptly inhibited. Reference is made to U.S. Pat. No. 3,857,385, Hampl, assigned to the assignee of this application, and to U.S. Pat. No. 4,259,967, Vooren et al., for general discussions of measuring respiratory resistance and parameters.